A wide array of apparatus and equipment are now employed to process semiconductor substrates. Some types of equipment, such as ion implantation machines, include portions which operate at relatively high voltages, e.g., 20,000 volts up into the million volt range. Sputtering equipment and dry etchers, for example, similarly employ one or more high voltage sections which are operated or controlled from a control station which is at or near ground potential.
Because high voltage sections of such equipment present a hazard to personnel and have the potential to damage low voltage portions of the control station, the high voltage equipment is normally spaced apart and physically isolated from the control station. In many instances, the high voltage components are contained within an isolated metal housing. Control signals generated at the control station are transmitted by ordinary, specifically dedicated electrical cables to the high voltage equipment section, and monitored data within the high voltage section is likewise transmitted through dedicated, hard wire cables back to the control station. Prior systems also employ a controller, typically in the form of a PC for controlling the exchange of data and control signals between the high voltage section and the control station.
The prior art system described above suffers from a number of disadvantages. First, interconnecting the control station with the high voltage equipment section using conductive wiring increases the possibility of a short circuits, the generation of electromagnetic interference (EMI), and potential damage to sensitive, low voltage equipment in the monitoring station as a result of arc over or other high voltage shorts passing through the communication cable. Also, the prior art system was expensive to implement and was not well suited to be modified or upgraded. The number of signals carried by the conductive interconnecting cable was limited. Finally, the system lacked flexibility in that incompatibilities existing between the operating voltages used by equipment items could not be easily accommodated, but once wired to accommodate these different voltages, was difficult if not impossible to reconfigure.
The present invention is directed toward overcoming each of the deficiencies inherent in the prior art discussed above.
Accordingly, it is a primary object to provide a flexible control system employing a communication link between high voltage equipment and a control station that is at or near ground potential.
Another object of the invention is to provide a control system as described above which utilizes a fiber optic communication link to effect high voltage isolation of the control station from the high voltage equipment.
A still further object of the present invention is to provide a system as described above which employs a pair of relatively simple, inexpensive controllers respectively in the areas of the high voltage equipment and control station, which is highly flexible and adaptable to monitor and operate controllable elements operating at different voltages.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.